Optical waveguide plate of surface light emitting apparatus

ABSTRACT

To provide an optical waveguide that can emit light of which intensity is uniformly distributed over the light emitting surface and can suppress the occurrence of the bright line, the optical waveguide of surface light emitting apparatus has a light emitting plane and a reflecting plane that oppose each other, the reflecting surface having a plurality of dots formed thereon so that light entering from a light source that is provided on one end face or two opposing end faces is output through the light emitting surface with uniform intensity, wherein the dots are arranged so as to form band regions each being defined as a region that has a constant density of distribution, a plurality of vertical lines of the dots are formed at substantially equal intervals in each of the band regions in the direction toward adjacent bands, and the interval between the vertical lines of dots is made different in different bands.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical waveguide plate of asurface light emitting apparatus used for spreading light from a lightsource over the entire light emitting surface and emitting the light.

[0003] 2. Description of the Related Art

[0004] Such surface light emitting apparatus have recently been used asthe light source for backlight of liquid crystal display, that outputslight from a point source such as LED chip by spreading the light over aplane. In the surface light emitting apparatus, light emitted by one ormore light emitting diode enters through one end of an optical waveguideplate that has opposing principal planes, and exits through the wholearea of the other principal plane of the waveguide.

[0005] The surface light emitting apparatus has such a constitution asshown in a plan view of FIG. 20, comprising a casing 903, an opticalwaveguide plate 901 made of a transparent resin that has a firstprincipal plane and a second principal plane, a light emitting diode 902mounted so as to oppose the end face of the optical waveguide plate 901,and a reflector (not shown) mounted on the second principal plane of theoptical waveguide plate, so that light emitted by the light emittingdiode 902 is output through the entire area of one principal plane ofthe optical waveguide plate 901.

[0006] In the surface light emitting apparatus having the constitutiondescribed above, since light emitted by the light emitting diode 902 isattenuated while being transmitted through the optical waveguide plate901, with the light intensity decreasing in inverse proportion to thedistance from the light source, a light diffusion dot pattern is formedon the second principal plane that serves as the reflector so as toobtain light output uniformly distributed over the plane. The lightdiffusion dot pattern makes the luminance distribution uniform over thelight emitting surface by increasing the density of dots or the area ofeach dot with the distance from the light source, thereby increasing thearea occupied by the light diffusing dots.

[0007]FIG. 21 is a plan view showing light diffusion dot pattern of areflecting surface of the optical waveguide plate disclosed in JapaneseUnexamined Patent Publication (KOKAI) No. 8-271893. In this example,area of each of dots 102 is increased with the distance from a lightsource 101, thereby gradually increasing the proportion of area occupiedby the light diffusing dots as the distance from the light sourceincreases.

[0008] With the light diffusion dot pattern of the prior art shown inFIG. 21, however, there has been the problem of bright line generateddue to the arrangement of the light diffusing dots.

SUMMARY OF THE INVENTION

[0009] Thus, an object of the present invention is to provide an opticalwaveguide that can emit light of which intensity is uniformlydistributed over the light emitting surface and can suppress theoccurrence of the bright line.

[0010] In order to achieve the object described above, the opticalwaveguide of a first surface light emitting apparatus of the presentinvention has a light emitting plane and a reflecting plane that opposeeach other, with the reflecting surface having a plurality of dotsformed thereon so that light entering from a light source that isprovided on one end face or two opposing end faces is output through thelight emitting surface with uniform intensity, wherein the dots arearranged so as to form band regions each being defined as a region thathas a constant density of distribution, a plurality of vertical lines ofthe dots are formed at substantially equal intervals in each of the bandregions in the direction toward adjacent bands, and the interval betweenthe vertical lines of dots is made different in different bands.

[0011] In the optical waveguide of the first surface light emittingapparatus of the present invention having the constitution describedabove, since the interval between the vertical lines is made differentbetween adjacent bands, there is no vertical line extending over a longdistance and the occurrence of bright line can be prevented.

[0012] The optical waveguide of a second surface light emittingapparatus of the present invention has a light emitting plane and areflecting plane that oppose each other, with the reflecting surfacehaving a plurality of dots formed thereon so that light entering from alight source provided on one end face or two opposing end faces isoutput through the light emitting surface with uniform intensity,wherein the dots are arranged so as to form band regions each beingdefined as a region that has a constant density of distribution, aplurality of vertical lines of the dots are formed at equal intervals ineach of the band regions in the direction toward adjacent bands, and thedots are arranged in two adjacent band regions so that the verticallines of dots in one band region and the vertical lines of dots in theother band region do not lie in the same straight lines.

[0013] In the optical waveguide of the second surface light emittingapparatus of the present invention having the constitution describedabove, since the dots are arranged in two adjacent band regions so thatthe vertical lines of dots in one band region and the vertical lines ofdots in the other band region do not lie in the same straight lines,there is no vertical line extending over a long distance and theoccurrence of bright line can be prevented.

[0014] In the optical waveguides of the first and second surface lightemitting apparatus of the present invention, such a constitution mayalso be employed as the dots are arranged so that a plurality ofhorizontal lines are formed at right angles to the vertical lines ineach of the band regions, while the interval between the vertical linesand the interval between the horizontal lines are determined inaccordance to the density of dots in the band region.

[0015] An optical waveguide of the third surface light emittingapparatus of the present invention has a light emitting plane and areflecting plane that oppose each other, with the reflecting surfacehaving a plurality of dots formed thereon so that light entering from alight source that is provided on one end face or two opposing end facesis output through the light emitting surface with uniform intensity,wherein the dots are arranged so as to form the band region that isdefined as a region where the dots are distributed with uniformdistribution, with the concentration of dots being different betweenadjacent band regions, and the dots are disposed at lattice points of alattice consisting of square cells in each of the band regions.

[0016] In the optical waveguides of the third surface light emittingapparatus of the present invention having the constitution describedabove, since every band region has the dots distributed in differentdensity therein than in the adjacent band regions and the dots aredisposed at lattice points of the lattice consisting of square cells ineach of the band regions, the distance between adjacent dots arranged inthe lattice pattern is different between adjacent band regions.

[0017] Thus the interval between the vertical lines of dots is madedifferent in the adjacent band regions in the optical waveguides of thethird surface light emitting apparatus, and therefore there is novertical line extending over a long distance, and the occurrence ofbright line can be prevented, similarly to the first surface lightemitting apparatus.

[0018] In the optical waveguides of the first through third surfacelight emitting apparatus of the present invention, density of dots ineach band region is preferably changed according to the attenuation oflight transmitted from the light source so that a region that receiveslight with greater attenuation has the dots in higher density, whichenables it to emit light with uniform intensity.

[0019] In the optical waveguides of the first through third surfacelight emitting apparatus of the present invention, such a constitutionmay also be employed as the dots are arranged randomly in a density thatis set according to the attenuation of light, in part of the reflectorsurface located on both sides of the end face where the light source ismounted.

[0020] Moreover, in the optical waveguides of the first through thirdsurface light emitting apparatus of the present invention, it ispreferable that the dot has a concave portion and a convex portion,which enable the dot to diffuse light more effectively.

[0021] Each dot may be constituted either from a convex portion and aconcave portion that surrounds the former, or from a concave portion anda convex portion that surrounds the former

[0022] As described above, in the optical waveguide of the surface lightemitting apparatus according to the present invention, since the dotsare arranged so as to form band regions each being defined as a regionthat has a constant density of distribution and no vertical line extendsover a long distance across adjacent band regions, the occurrence ofbright line can be prevented.

[0023] Also according to the present invention, the dots may be randomlydistributed in such a proper density required to prevent the occurrenceof bright lines, thereby to effectively prevent the occurrence of brightlines.

[0024] Therefore, the present invention can provide the opticalwaveguide that is capable of emitting light uniformly through the lightemitting surface, and suppressing the occurrence of bright lines.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a plan view showing the distribution of dots formed on areflecting surface of an optical waveguide plate according to firstembodiment of the present invention.

[0026]FIG. 2 is an enlarged plan view of a part 51 of FIG. 1.

[0027]FIG. 3 is a graph showing the density distribution of dots formedon the reflecting surface of the optical waveguide plate according tothe first embodiment.

[0028]FIG. 4 is a plan view showing the dots formed in a lattice patternin each band region by a method of setting the dot pattern according tothe first embodiment

[0029]FIG. 5 is a plan view showing the distribution of dots formed on areflecting surface of an optical waveguide plate according to secondembodiment of the present invention.

[0030]FIG. 6 is a flow chart of light diffusion pattern creating methodin a region 53 according to the second embodiment of the presentinvention.

[0031]FIG. 7 shows an example of a table showing the numbers of dotsrequired in different regions, determined in step S3 of the lightdiffusion pattern creating method according to the second embodiment ofthe present invention.

[0032]FIG. 8 is a plan view showing the reflecting surface of theoptical waveguide plate divided in a mesh pattern determined in step S3of the light diffusion pattern creating method according to the secondembodiment of the present invention.

[0033]FIG. 9A shows circles drawn in correspondence to the dots of themaximum number that can be placed in each cell in step S5 of the lightdiffusion pattern creating method according to the second embodiment,and FIG. 9B shows the state of the required number of circles left ineach cell by deleting redundant dots from the circles that have beenplaced in each cell in close-packed arrangement in step S5, thereby toleave the circles of the number required in each cell in step S6.

[0034]FIG. 10A shows the positions to place the dots being determined sothat the maximum number of dots can be placed in each cell without anydots overlapping each other, in the light diffusion pattern creatingmethod according to a variation of the present invention, and FIG. 10Bshows a state after the required number of dots that has been determinedin step S3 are randomly placed in each cell where the positions to placethe dots have been determined.

[0035]FIG. 11 is a plan view showing the range of a region 53 in thesecond embodiment.

[0036]FIG. 12 is a plan view showing the region 53 that is set in arange different from that shown in FIG. 11 according to the secondembodiment.

[0037]FIG. 13 is a plan view showing the direction of light propagationin the second embodiment.

[0038]FIG. 14 shows the shape of dot (variation 1) that can be employedin the optical waveguide plate according to the present invention, in asectional view and a plan view.

[0039]FIG. 15 shows the shape of dot (variation 2) that can be employedin the optical waveguide plate according to the present invention, in asectional view and a plan view.

[0040]FIG. 16 shows the shape of dot (variation 3) that can be employedin the optical waveguide plate according to the present invention, in asectional view and a plan view.

[0041]FIG. 17 shows the shape of dot (variation 4) that can be employedin the optical waveguide plate according to the present invention, in asectional view and a plan view.

[0042]FIG. 18 shows the shape of dot (variation 5) that can be employedin the optical waveguide plate according to the present invention, in asectional view and a plan view.

[0043]FIG. 19 shows the shape of dot (variation 6) that can be employedin the optical waveguide plate according to the present invention, in asectional view and a plan view.

[0044]FIG. 20 is a plan view of a common surface light emittingapparatus.

[0045]FIG. 21 is a plan view showing a n example of dot pattern formedon the reflecting surface of an optical waveguide plate of the priorart.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Now the optical waveguide plate of the surface light emittingapparatus according to preferred embodiments of the present inventionwill be described below with reference to the accompanying drawings.

[0047] First Embodiment

[0048] The first embodiment of the present invention provides an opticalwaveguide plate of a surface light emitting apparatus having such aconstitution that light emitted by a light source is output with uniformintensity through a light emitting surface by forming a multitude ofdots in a predetermined pattern on a reflecting surface that is aprincipal plane opposing another principal plane serving as the lightemitting surface, wherein the dots are distributed in a pattern uniqueto the present application.

[0049] Specifically, the optical wavegudie of the first embodiment hasthe dots formed as described below in major portions of the reflectingsurface except for corners 52, 52 b located at both sides of the endface where a light source 10 is provided.

[0050]FIG. 1 is a plan view showing the distribution of the dots formedon the reflecting surface of the optical waveguide plate, and FIG. 2 isan enlarged view of a part (indicated by numeral 51) of FIG. 1.

[0051] (Band Region where Dots are Distributed in Constant Density)

[0052] In the reflecting surface of the first embodiment, the dots arearranged so that the area where the dots are uniformly distributed formsa band region as shown in FIG. 2.

[0053] The band region R_(k) (k=1, 2, 3, . . . , n) are defined bysetting a border line every time the density of dots is increased by ΔDyin the dot density curve C1 shown in FIG. 3.

[0054] Density of dots distributed in a band region R_(k) may be set toa dot density D_(k) that is the mean value of the maximum density andthe minimum density on the dot density curve C1 of the particularregion, while the dots are formed with uniform density within each bandregion R_(k) (the dot density D_(k) is the same anywhere in the bandregion R_(k)).

[0055] In another word, a band region R_(k) is defined as a region thathas a constant concentration of distribution.

[0056] In the first embodiment, width ΔLx_(k) of a band region R_(k) isset to a sufficiently small value compared to the length of the opticalwaveguide plate, so that the density of dots in the first embodiment canbe effectively considered to be equivalent to that determined accordingto the dot density curve C1 shown in FIG. 3, even when the density ofdots is set uniform within each band region R_(k).

[0057] (Arrangement of Dots in each Band Region R_(k))

[0058] In the band region R_(k) of the first embodiment, the dots arearranged so as to form vertical lines 1 _(k) in the direction toward theadjacent band region (the longitudinal direction of the opticalwaveguide plate in the case of the first embodiment) as shown in FIG. 2.

[0059] Also in each band region R_(k), dots are arranged so as to form aplurality of horizontal lines 2 _(k) that are perpendicular to thevertical lines 1 _(k).

[0060] The distance between the vertical lines 1 _(k) and the distancebetween the horizontal lines 2 _(k) are determined so as to meet therequirement of the dot density D_(k) for the band region R_(k).

[0061] (Dot Arrangement Required in Adjacent Band Regions R_(k),R_(k+1))

[0062] In the first embodiment, the distance between the vertical line 1_(k) of dots formed in each band region R_(k) is made different from thedistance between the vertical line 1 _(k+1) of dots formed in theadjacent band region R_(k+1).

[0063] Also the dots are arranged so that the vertical line 1 _(k) ofthe dots formed in a band region R_(k) and the vertical line 1 _(k+1) ofthe dots formed in a band region R_(k+1)adjacent therewith do not lie ina single straight line.

[0064] Also according to the present invention, it is preferable toincrease the distance between the vertical line 1 _(k) of a band regionR_(k) and the vertical line 1 _(k+1) of the adjacent band region R_(k+1)where bright line is likely to occur, so as to enable it to effectivelysuppress the occurrence of the bright line. Accordingly, the verticalline 1 _(k+1) of the band region R_(k+1) is preferably located on thecenter line of the adjacent vertical line 1 _(k) of the band regionR_(k) in the vicinity of the extended line of the optical axis of thelight source on the reflecting surface of the optical waveguide plate.

[0065] Thus according to the first embodiment, since the distancebetween the vertical line 1 _(k) in the band region R_(k) is madedifferent from the distance between the vertical line 1 _(k+1) in theadjacent band region R_(k+1) and the vertical line 1 _(k) in the bandregion R_(k) and the vertical line 1 _(k+1) in the band region R_(k+1)are arranged so as not to lie in a single straight line, the occurrenceof bright line can be prevented.

[0066] That is, while the dots are arranged along straight lines inevery band region R_(k) in the first embodiment, every band region R_(k)is limited within a definite area and therefore the dots never lie on along straight line that extends beyond the band region R_(k), so thatthe dots lying on straight lines in the band region R_(k) do notgenerate perceptible bright lines.

[0067] Thus in the first embodiment, the dots can be prevented frombeing undesirably distributed by arranging the dots according to acertain rule in each band region R_(k), and the occurrence of brightline is prevented by changing the rule of arranging the dots betweenadjacent band regions.

[0068] While the distance between the vertical line 1 _(k) in the bandregion R_(k) is made different from the distance between the verticalline 1 _(k+1) in the adjacent band region R_(k+1) and the vertical line1 _(k) in the band region R_(k) and the vertical line 1 _(k+1) in theband region R_(k+1) are arranged so as not to lie in a single straightline in the first embodiment, the present invention is not limited tothis constitution and positions of the vertical line in each band regionmay be determined so as to meet either one of the conditions.

[0069] That is, when the distance between the vertical line 1 _(k) inthe band region R_(k) is made different from the distance between thevertical line 1 _(k+1) in the adjacent band region R_(k+1) and thevertical line 1 _(k+1) in the band region R_(k+1) the dots hardly lie ona straight line that extends over three band regions R_(k), R_(k+1),R_(k+2), although some dots may lie on a straight line that extendsacross two adjacent band regions R_(k), R_(k+1). Therefore, according tothe present invention, operations and effects similar to those of thefirst embodiment can be achieved simply by making the distance betweenthe vertical line 1 _(k) in the band region R_(k) different from thedistance between the vertical line 1 _(k+1) in the adjacent band regionR_(k+1).

[0070] Also in one band region R_(k), when the dots are arranged so thatthe distance between the vertical line 1 _(k) near the central portionis made different from the distance between the vertical line 1 _(k+1)in portions away from the central portion, operations and effectssimilar to those of the first embodiment can be achieved simply byemploying such an arrangement as the vertical line 1 _(k) of the bandregion R_(k) and the vertical line 1 _(k+1) of the band region R_(k+1)do not lie on the same line.

[0071] (Arrangements of Dots in Corners 52 a, 52 b of the ReflectingSurface)

[0072] On the reflecting surface of the optical waveguide plateaccording to the first embodiment, the dots are arranged randomly in apredetermined density in the corners 52 a, 52 b located on both sides ofthe end face where the light source 10 is mounted.

[0073] The corners 52 a, 52 b receives less light due to the directivityof the light and tend to be darker, and therefore require higher densityof dots than other portions. Since it is not necessary to arrange thedots in accordance to the predetermined rule in these portions, the dotsare arranged randomly in the corners 52 a, 52 b in the first embodiment.

[0074] Random arrangement in the predetermined density may be also beachieved in the corners 52 a, 52 b by arranging the dots according to arule similar to that for the band region and then adding the dotsrandomly.

[0075] Now an example of the method of setting the dot pattern accordingto the first embodiment will be described below.

[0076] (Step 1)

[0077] According to this method, first, the dot size is determined bygiving consideration to the shape of the optical waveguide plate and themanufacturing method to be employed in forming the dots.

[0078] (Step 2)

[0079] Then the dot area ratio (proportion of the area occupied by thedots to the unit area) at each position on the reflecting surface, sothat the light intensity distribution is uniform over the light emittingsurface. The dot area ratio is set in accordance to the attenuation ofthe light, so as to be higher in a portion where light is subjected tohigher attenuation.

[0080] Based on the dot area ratio and the dot size determined in step1, a dot density curve (C1 shown in FIG. 3) is drawn.

[0081] (Step 3)

[0082] Then the band region R_(k) (k=1, 2, 3, . . . , n) are defined bysetting the border line every time the density of dots is increased byΔDy according to the dot density curve (C1 shown in FIG. 3) that hasbeen drawn in step 2, thereby to set the density of dots in each bandregion R_(k) to, for example, the mean value of the maximum density andminimum density on the dot density curve C1 of the particular region.

[0083] (Step 4)

[0084] Then each band region R_(k) is divided into cells as shown inFIG. 4 according to the dot density D_(k) that has been set for eachregion, and one dot is placed at the center of each lattice La_(k). Thatis, one dot is formed in each lattice La_(k) and the size of the latticeLa_(k) is determined so as to achieve the dot density D_(k) in the bandregion R_(k).

[0085] More specifically, area SLa of each cell is determined byequation (1) and length P of one side of the cell is determined as thesquare root of the area (equation (2)).

Area SLa=(Unit area)/(Dot density D_(k))   (1)

Length P of cell side={square root} (Area SLa)   (2)

[0086] Once the arrangement of dots is determined as described above,length of the cell on one side thereof is different between the adjacentband regions R_(k), R_(k+1) due to the different density of dots, andtherefore the distance between the vertical line 1 _(k) of the bandregion R_(k) and the distance between the vertical line 1 _(k+1) of theband region R_(k+1) are set to different values.

[0087] Thus the dots can be arranged so that the vertical line 1 _(k) ofthe band region R_(k) and the vertical line 1 _(k+l) of the band regionR_(k+1) do not lie on the same straight line, thereby preventing theoccurrence of bright line.

[0088] While some dots may lie on a straight line that extends acrosstwo adjacent band regions when the arrangement of dots is determined asdescribed above, the probability is nearly zero for the dots to lie onone straight line that extends across three band region, and thereforethe occurrence of perceptible bright lines can be prevented.

[0089] Needless to say, the dots arranged as described above form a newlattice consisting of lattice points located at the center of each cellof the lattice that separates the band region.

[0090] In the optical waveguide plate of the surface light emittingapparatus of the first embodiment described above, the dots are arrangedby defining the band regions over the entire surface of the reflectingsurface except for the corners 52 a, 52 b.

[0091] However, the present invention is not limited to the constitutiondescribed above, and the dots may also be arranged so as to prevent theoccurrence of bright line more effectively in the portion of thereflecting surface near the light source where bright line tends tooccur more conspicuously (for example, the portion denoted by 51 in FIG.1).

[0092] Second Embodiment

[0093] An optical waveguide plate of the second embodiment will bedescribed below.

[0094] The optical waveguide plate of the second embodiment has the dotsarranged randomly on the side of end face where the light source 10 ismounted, so as to prevent the occurrence of bright line more effectivelythan the optical waveguide plate of the first embodiment.

[0095] Specifically in the optical waveguide plate of the secondembodiment, the dots are arranged on the side of end face where thelight source 10 is mounted so that the required density of dots issatisfied in the region 53 in front of the light source 10 and in thecorners 52 a, 52 b located on both sides of the region 53, and the dotsare arranged similarly to the first embodiment in the region 53 and inthe region 57 (region away from the end face where the light source 10is mounted) except for the corners 52 a, 52 b.

[0096] Now the arrangement of dots in the region 53 and in the corners54 a, 54 b according to the second embodiment of the present inventionwill be described in detail below.

[0097] In alight diffusion dot pattern on the reflecting surface of theoptical waveguide plate of the second embodiment, dots are randomlydistributed so as not to lie on the same straight line with the densityof dots increasing with the distance from the light source 10 in theregion 53 to compensate for the attenuation of the light emitted by thelight source, thereby suppressing the occurrence of bright line in thelight emitting surface of the optical waveguide plate (particularly inthe vicinity of the light source 10).

[0098] In the second embodiment, density of dots in the region 53 is setaccording to the dot density curve shown in FIG. 3 that has beendescribed in the first embodiment.

[0099] Now the light diffusion dot pattern for the region 53 in thesecond embodiment will be described below with reference to the flowchart shown in FIG. 6.

[0100] In step S1 of this method, data related to the optical waveguideplate required for creating the light diffusion dot pattern are inputincluding the shape of the optical waveguide plate, entering position oflight (mounting position of the light source) and shape and dimensionsof the dots.

[0101] In step S2, numbers of vertical and horizontal divisions of thereflecting surface of the optical waveguide plate are determined inaccordance to the data related to the optical waveguide plate (the shapeof the optical waveguide plate and shape and dimensions of the dots)that have been input in step S1.

[0102] When determining the numbers of vertical and horizontaldivisions, it is preferable to set the length of one side of the dividedcell to a multiple of the diameter or approximately thereto. This makesit possible to form the dots without empty space in a cell and withoutempty space between the dots of adjacent cells.

[0103] Also according to the present invention, in order to change thedensity of dots smoothly, the numbers of horizontal and verticaldivisions are preferably determined so that the divided cells aresubstantially square and the maximum number of dots that can be formedin the divided cells satisfies the condition described below.

[0104] In case the dot is round, the division is carried out so that theproduct of the maximum number of dots that can be placed in each celland the dot diameter is from 5 to 10 (mm·number)

[0105] In case the dot is square, the division is carried out so thatthe product of the maximum number of dots that can be placed in eachcell and the width of the dot is from 5 to 10 (mm·number).

[0106] The procedure of step S2 is as follows, for example, when theoptical waveguide plate measures 66 mm vertically and 18 mm horizontallyand the dot is a circle 60 μm in diameter.

[0107] First, preferable range of the maximum number of dots isdetermined as 83 to 167 (5 to 10 mm·number/0.06 mm) based on thecondition described above.

[0108] Then preferable number of dots to be placed along one side of thesubstantially square region is determined to be from 9 to 13 from thepreferable range of the maximum number of dots.

[0109] Length of one side of the region is determined in accordance tothe product of the preferable number of dots to be placed along one sideof the region (9 to 13) and the dot diameter 0.06 mm.

[0110] In the case of the optical waveguide plate having the dimensiondescribed above, it is divided by 100 into parts each measuring 0.660 mmin the vertical direction and divided by 30 into parts each measuring0.600 mm in the horizontal direction With this division, 110 dots can beplaced side by side without space by placing 11 dots in the verticaldirection and 10 dots in the horizontal direction. This division alsomakes it possible to arrange the dots without empty space between thedots in the adjacent regions.

[0111] In step S3, required number of dots to be formed in each regionthat has been divided in step S2 is determined in accordance to theattenuation of light on the optical waveguide plate.

[0112] Specifically, density function is defined for the attenuation oflight on the optical waveguide plate, and the required number of dots tobe formed in each region is determined from the density function.

[0113] The density function represents the density distribution of dotsas a function of the distance from the light source and the direction(namely the position on the reflecting surface) on the reflectingsurface of the optical waveguide plate, and has a small value near thelight source where light is less attenuated and has a large value awayfrom the light source where light is more attenuated. The densityfunction also increases with the angle from the optical axis of thelight source, and decreases as the angle from the optical axis of thelight source decreases.

[0114] Density function for a constitution having a plurality of lightsources can be created by adding the density function for each lightsource.

[0115]FIG. 7 shows an example (in the case of division by 5 in bothvertical and horizontal directions) of table of the required number ofdots to be formed in each region that has been determined in step S3. Inthe example shown in FIG. 7, the light source is placed in front of theregion located at row 1 and column 3.

[0116] In step S4, the reflecting surface of the optical waveguide plateis divided into cells according to the number of divisions determined instep S2 on, for example, a computer display.

[0117]FIG. 8 shows an example of mesh having 25 cells (5×5) from M11through M55 according to the division shown in FIG. 7.

[0118] In step S5, circles having diameter of R that represent the dots(referred to dot 21) are drawn by the maximum number of dots that can beplaced in each cell (close-packed arrangement).

[0119] Then in step S6, redundant dots are randomly deleted from thedots 21 that have been placed in each cell in close-packed arrangementin step S5, thereby to leave the dots 21 of the number required in eachcell (the number determined for each cell in step S3).

[0120] Thus the circles are drawn representing the number of requireddots randomly arranged in each cell.

[0121] Such a light diffusion dot pattern is thus created as the densityof dots increases with the distance from the light source so as tocompensate for the attenuation of light and the dots are randomlyarranged so as not to lie on straight lines.

[0122] In step S5 and step S6 of the second embodiment described above,redundant circles may be randomly deleted from the circles that havebeen placed in close-packed arrangement for each cell in step S6 afterdrawing the maximum number of circles in all cells or, alternatively,after drawing the maximum number of circles in one cell in step S5,redundant circles may be randomly deleted from the circles that havebeen placed in the cell in step S6 and then repeating the operations ofsteps S5 and S6 for every cell.

[0123] Variation of Second Embodiment

[0124] In the light diffusion pattern creating method of the secondembodiment described above, circles representing the dots are placed ineach cell in step S5 and redundant circles are randomly deleted from thecircles of each cell in step S6, but the present invention is notlimited to this procedure. Step S5 and step S6 may be replaced with theprocedure described below.

[0125] Positions 22 for placing dots are determined in each cell so asto pace the maximum number of dots in each cell without any dotsoverlapping each other as shown in FIG. 10A.

[0126] The dots 21 having diameter of R are placed randomly by therequired umber determined in step S3 in each cell where the positions toplace the dots have been determined, as shown in FIG. 10B.

[0127] This procedure also creates such a light diffusion dot pattern asthe density of dots increases with the distance from the light source soas to compensate for the attenuation of light and the dots are randomlyarranged so as not to lie on straight lines.

[0128] According to the methods for creating the light diffusion dotpattern of the second embodiment and the variation of the secondembodiment, the light diffusion dot pattern capable of suppressing theoccurrence of bright line in the light emitting surface can be createdeasily in a short period of time.

[0129] Although the circular dots are used in the second embodiment, thepresent invention is not limited to this constitution and the dots mayhave rectangular or other shape.

[0130] Effects similar to those of the second embodiment can also beachieved in this way.

[0131] In this case, the light diffusion dot pattern consisting ofrectangular dots may be formed so that the centers of the rectangulardots coincide with the centers of the circular dots of the lightdiffusion dot pattern created in steps S1 through S6.

[0132] In the method of creating the light diffusion dot patternaccording to the second embodiment, circular dots are placed side byside without space therebetween, but the present invention is notlimited to this constitution. For example, the present invention mayalso be applied to a case where dots having diameter of r (r<R) areplaced with a predetermined distance from each other.

[0133] In this case, too, the light diffusion dot pattern consisting ofdots placed with a predetermined distance from each other may be formedso that the centers of the circular dots having diameter of r smallerthan R coincide with the centers of the circular dots having diameter Rplaced side by side without space therebetween in the light diffusiondot pattern created in steps S1 through S6.

[0134] In this case, the distance between adjacent dots that are placemost closely to each other is (R-r) within a cell as well as betweenadjacent cells.

[0135] (Setting the Region 53 where Dots are Placed Randomly)

[0136] The region 53 where dots are placed randomly in the secondembodiment is set as follows.

[0137] In the second embodiment, random arrangement of the dots isapplied to the portion where the bright line is most likely to occur, asdescribed above.

[0138] Thus the position where the dots are to be randomly placed can bedefined by a circle having center at the light emitting point of thelight source 10, considering the fact that the portion where bright lineis most likely to occur is within a particular distance from the lightsource 10.

[0139] Specifically, a semicircle C53 having a diameter equal to thewidth of the optical waveguide plate is drawn with the center located atthe center of the end face where the light source 10 is mounted, asshown in FIG. 11, and the portion inside of the semicircle C53 exceptfor the corners 54 a, 54 b is defined as the region 53 where the dotsare to be randomly placed. Brightness distribution over the lightemitting surface of the optical waveguide plate can be made extremelyuniform when the arrangement described in the first embodiment isapplied to the other portions except for the region 53 and the corners54 a, 54 b.

[0140] The reason for omitting the corners 54 a, 54 b from thesemicircle C53 is the fact that bright line is less likely to occur inthe corners 54 a, 54 b due to the directivity of the light source 10. Inthe corners 54 a, 54 b, luminance of the light is lower (light isattenuated more) than in the other portion due to the directivity of thelight source 10, and therefore the number of dots is preferablyincreased according to the degree of attenuation of light.

[0141] In the corners 54 a, 54 b, dots may be arranged either randomlyor regularly, as long as the desired density is satisfied.

[0142] In case the region 53 where the dots are to be randomly placed isdefined as shown in FIG. 11, the portion where bright line is likely tooccur varies depending on the directivity of the light source or otherfactor, and the diameter of the semicircle C53 may be made smaller thanthe width of the optical waveguide plate in accordance to thecharacteristic of the light source.

[0143] According to the second embodiment, definition of the region 53shown in FIG. 12 may be employed instead of the fan-shaped region 53shown in FIG. 11.

[0144] That is, the region 53 maybe defined as the region located nearerto the light source than a border line T53 that is parallel to the endface where the light source is mounted and is a tangential line of thesemicircle C53 shown in FIG. 11 minus the corners 54 a, 54 b in FIG. 12.

[0145] In this case, the region 53 may also be defined by the borderline T53 a that is a translation of the border line T53 moved 0 to 5 mmaway from the light source.

[0146] In the portion (indicated with numeral 58 in FIG. 13) that ismore distant from the light source than the region 53 that is defined asdescribed above, light that has reflected on the side face and lighttransmitted directly from the light source are mixed, therebysuppressing the occurrence of bright line.

[0147] According to the present invention, as described above, theoccurrence of bright line can be prevented by placing the dots in randomarrangement in such a portion where the bright line is most likely tooccur due to the influence of directivity of the light source.

[0148] Variation

[0149] (Shape of Dots)

[0150] According to the present invention, the dots may comprise eitherconcave or convex, and may have various shape to be described later.

[0151] Preferable dot shapes that can be employed in the presentinvention will now be described below with reference to FIG. 14 throughFIG. 19. In each of FIG. 14 through FIG. 19, A is a sectional view and Bis a plan view.

[0152] The present invention is not limited to the dot shapes shown inFIG. 14 through FIG. 19 and various other shapes can also be employed.

[0153]FIG. 14 shows a dot consisting of a relatively simple recess froma datum reflection surface Rf, that can be easily made.

[0154]FIG. 15 shows a dot consisting of a ring-shaped ridge rising abovethe datum reflection surface Rf, and FIG. 16 shows a dot consisting ofthe recess shown in FIG. 14 that us surrounded by a ridge. The dotsshown in FIG. 15 and FIG. 16 have higher effect of diffusing light thanthe simple recess shown in FIG. 14.

[0155]FIG. 17 shows a dot consisting of a relatively simple bulge risingfrom the datum reflection surface Rf, that can be easily made.

[0156]FIG. 18 shows a dot consisting of a recess from the datumreflection surface Rf with a bulge at the center of the recess, and FIG.19 is a dot consisting of the bulge shown in FIG. 17 surrounded by arecess. The dots shown in FIG. 18 and FIG. 19 have higher effect ofdiffusing light than the simple recess shown in FIG. 17.

[0157] The dots shown in FIG. 15, FIG. 16, FIG. 18 and FIG. 19consisting of a convex and a concave and having higher effect ofdiffusing light can be made relatively easily by, for example, makinguse of such a phenomenon as making a hole by pressing a pointed pinagainst a resin plate is accompanied by the formation of a ridgesurrounding the hole. With this method, high reproducibility can beensured by controlling the pressing force. This method can also beembodied with a die that has a multitude of pins, thus allowing for massproduction.

[0158] According to the present invention, when the fact that lightdiffusing capability of the dot varies depending on the shape of the dotis made use of, brightness at every portion of the light emittingsurface can be adjusted including the density and arrangement of dotsdescribed in first and second embodiments and the shape of each dot.This makes it possible to make fine adjustment of brightness of thelight emitting surface that cannot be made simply by changing thedensity and arrangement of dots.

[0159] Particularly in the corners 54 a, 54 b that receive light oflower intensity and in portions having larger distance from the lightsource and tend to be dark, where sufficient luminance cannot beachieved by changing the density and arrangement of dots, light can bediffused effectively by selecting the dot shape, thereby improving theluminance.

[0160] Although FIG. 14 through FIG. 19 show dots having round shape inplan view, the present invention is not limited to this shape, andrectangular, polygonal or other shapes may also be employed.

[0161] In case circular dots are used in the first and secondembodiments, density of dots is preferably from 10 to 78.5% and whenrectangular dots are used, density of dots is preferably from 10 to100%.

[0162] Moreover, according to the present invention, the dots may havedifferent shapes in different regions according to the diffusion oflight required, which enables it to achieve more uniform distribution ofluminance over the light emitting surface.

What is claimed is:
 1. An optical waveguide plate of a surface lightemitting apparatus comprising a light emitting plane and a reflectingplane that oppose each other, said reflecting surface having a pluralityof dots so that a light inputted from a light source that is provided onone end face or two opposing end faces is output through said lightemitting surface with uniform intensity, wherein said dots are arrangedso as to form a plurality of band regions each of which is defined as aregion that has a constant distribution density, said each band regionhaving a plurality of vertical lines which are formed by the dots andare formed at substantially equal intervals in the direction towardadjacent band regions, said intervals between the vertical lines of dotsis set so as to be different between the adjacent band regions.
 2. Anoptical waveguide plate of a surface light emitting apparatus comprisinga light emitting plane and a reflecting plane that oppose each other,said reflecting surface having a plurality of dots so that a lightinputted from a light source that is provided on one end face or twoopposing end faces is output through said light emitting surface withuniform intensity, wherein said dots are arranged so as to form aplurality of band regions each of which is defined as a region that hasa constant distribution density and has a plurality of vertical lines ofthe dots that are formed at equal intervals in the direction towardadjacent band regions, wherein said dots are arranged in adjacent bandregions so that the vertical lines of dots in one band region and thevertical lines of dots in the other band region do not lie in the samestraight lines.
 3. The optical waveguide plates of a surface emittingapparatus according to claims 1 or 2; wherein said dots are arranged sothat a plurality of horizontal lines are formed perpendicular to saidvertical lines in said each band regions, the intervals between saidvertical lines and the intervals between said horizontal lines aredetermined in accordance to the density distribution of dots in eachband region.
 4. An optical waveguide plate of a surface light emittingapparatus comprising a light emitting plane and a reflecting plane thatoppose each other, said reflecting surface having a plurality of dots sothat a light inputted from a light source that is provided on one endface or two opposing end faces is output through said light emittingsurface with uniform intensity, wherein said dots are arranged so as toform a plurality of band regions each of which is defined as a regionthat has a constant distribution density and has a concentration of dotsbeing different between adjacent band regions, said dots being disposedat lattice points of a lattice consisting of square cells in each of theband regions.
 5. The optical waveguide plate as in one of claims 1, 2,4; wherein the density of said dots in each band region is changedaccording to the attenuation of light transmitted from the light source.6. The optical waveguide plate as in one of claims 1, 2, 4; wherein saiddots are arranged randomly in a density that is set according to theattenuation of light, in part of the reflector surface located on bothsides of the end face where the light source is mounted.
 7. The opticalwaveguide plates as in one of claims 1, 2, 4; wherein said dots arearranged randomly in a density that is set according to the attenuationof light, in part of the reflector surface adjacent to said lightsource.
 8. The optical waveguide plates as in one of claims 1, 2, 4;wherein the dot has a concave portion and a convex portion.
 9. Theoptical waveguide plate according to claim 8; wherein each dot isconstituted from a convex portion and a concave portion that surroundssaid convex portion.
 10. The optical waveguide plate according to claim8; wherein each dot is constituted from a concave portion and a convexportion that surrounds said concave portion.